Method of direct casting of steel slabs and billets



April 15, 1969 J, w, NORTH 3,438,424

METHoD 0F DIRECT CASTING oF STEEL sLABs AND BILLETS Original Filed Nov. 1*3, 1964 ATTORNEYS United States Patent O M' 3,438,424 METHOD OF DIRECT CASTING OF STEEL SLABS AND BILLETS John W. North, 643 Pine Tree Drive, Decatur, Ga. 30030 Original application Nov. 13, 1964, Ser. No. 410,938. Divided and this application July 18, 1967, Ser. No.

Int. Cl. Bzzc 3/00 U.S. Cl. 164-138 2 Claims ABSTRACT OF THE DISCLOSURE A throwaway replaceable ceramic lining for a -mold used in forming ingots, billets and steel slabs.

This application is a division of my copending application, Serial No. 410,938, led November 13, 1964, now abandoned.

The present invention relates to direct casting of steel slabs and billets and is concerned more particularly with an improved method for obtaining such steel slabs and billets with a minimum incorporation of foreign materials and defects in the cast surfaces of the billets.

The prior practice of direct casting of steel slabs and billets has involved the use of thick graphite mold with use of differential pressure technique in filling the mold and while this resulted in obtaining directly cast steel slabs and billets and the liks, their is certain inherent disadvantageous features, For example, the initial expense of the graphite mold, and the necessity of machining the cavity after a few castings are poured.

In the prior art casting ingots using the cast iron mold it is customary to coat the mold with mold wash such as an oxide of the metal being poured to prevent the steel from melting into the iron and welding. Due to the fact that the steel is poured at a temperature at least 600 F. hotter than the melting temperature of the gray iron molds, there is a significant number of cases of iron melting on the surface and the steel and the iron Welding together in spite of the mold coating. Due to this occurrence, plus normal thermal shock, the mold surface deteriorates and often the welding is so extensive that the mold is ruined.

Also the surface deterioration of the mold, the manner of applying coating, precipitation of gas in the ingots can, as in shock chills, and the cracks in the ingot from fast chilling, cause surface defects in the ingot which must be removed before rolling to prevent these defects from showing in the nished steel after complete rolling and finishing.

According to the present invention a new mold structure is provided and a new method of obtaining steel slabs, billets or ingots by direct casting in which the mold does not deteriorate significantly, because an inner liner of ceramic is provided as a preformed ceramic sheet and becomes a piece of low cost equivalent rather than a repeated expense. Due to the good heat-shock resistance of the ceramic liner the surface of the slab, billet or ingot is not shock chilled and lies against a smooth dry ceramic resulting in a surface practically free of significant defects. Also the metal shell of the mold together with the ceramic provide desirable heat flow control. The resulting economies and reliability in the casting system indicate economies in casting slabs, billets and ingots to essentially their desired dimensions, saving, in many cases, several times the cost of the non-reusable ceramic liners or the sprayed or other air applied ceramic coatings.

It is the object of the invention, therefore, to provide an Patented Apr. 15, 1969 improved apparatus and method for providing direct casting of steel slabs, billets or ingots.

Another object of the invention is to provide an improved method and apparatus which incorporates the use of a throw-away ceramic liner for each casing if required.

Still another object of the invention is to provide a ceramic liner which may be rebuilt to the desired thickness after use as required.

Other objects and advantages of the invention will be apparent from the following description of certain preferred embodiments thereof, taken in connection with the accompanying drawing, in which:

FIG. 1 is a schematic plan View of a mold for a direct casting of steel slabs, billets or ingots;

FIG. 2 is a transverse sectional view taken in the plane indicated by the line 2 2 in FIG. l;

FIG. 3 illustrates a modified mold structure.

Referring first to FIGS. 1 and 2 the mold of this invention comprises an outer shell 10 of metal such as sheet steel, aluminum, or copper of a desired thickness for structural purposes to form the side walls and bottom walls of mold, and this metal shell has angles 11 secured to the side thereof to support piping 12 having spray openings 13 therealong. This piping extends over the four sides and the bottom of the shell 10. Preferably, the cooling should maintain the ceramic liner at about 500 F. or less at its outer surface in contact with the metal shell. Inside the shell 10 there is provided a ceramic liner 1,5 in the form of replaceable rectangular sheets at the four sides and bottom of the mold, this ceramic being of high thermal shock resistance and capable of accepting :direct pouring of molten hot steel from a height of 20 to 30 feet. 'Ihese rectangular sheets may be adhesively secured inside of the shell 10 which has apertures 10a to provide for adhesive keys in securing the sheets in place. This ceramic material may comprise a pressed and dried unfired mixture of an aplastic material and sodium silicate. This ceramic liner is preferably of 1/s to v3/s inch in thickness and while the liners may be used :over in some cases, the expense 'of providing the liners is so small that they can be thrown away with each ingot.

FIG. 3 illustrates a modified mold construction in which the upper part of the mold is provided with a convergent ceramic portion 14 terminating in a central cylindrical opening 16. This reduced section at the top of the mold is pro-vided by ceramic moldings of frusto-conical contour at the bottom 17 and being secured in place by fastening bolts 18. The mold shown in FIG. 3 provides a hot top or feed for a killed steel ingot to maximize the percentage of the ingot or slab without shrink cavity or pipe. The removable top half of the mold is normally held in place by means of a typical C clamp 19 although any other suitable detachable fastening means may be employed. Above the molten steel in FIG. 3 there is provided a layer of hot topping compound.

In carrying out the method disclosed here in which a thin ceramic layer is employed between the molten metal and the sheet metal shell of the mold, the controlled constant cooling provides important advantages as compared with a thick cast iron mold. For example, a uniform ow of British termal units is obtained through this ceramic layer and the sheet metal layer from a temperature differential of about Z600 F. at the surface of the molten metal to about 500 to 125 F. at the outside surface of the sheet metal shell of the mold. This provides faster over all cooling as compared with a thick cast iron mold where the rate of initial flow of British thermal units will be substantially higher but as theI cast iron mold becomes hot there is a substantially reduced rate of liow.

In practice a desired outside temperature is selected in accordance with the characteristics of the steel being poured and the coolant being used. Also, the thickness of the ceramic coating or liner can be selected to control the desired rate of cooling and is selected in accordance with the characteristics of the particular steel being poured. For example, with air cooling it may be desirable to employ higher temperatures of 550 F. or lower in pouring steels such as high carbon steels or hard alloy steels which are damaged by too rapid cooling. With a liquid coolant such as water, lower temperatures of 212 to 125 F. may be employed in pouring ordinary low carbon steels.

The use of the thin ceramic lining as disclosed herein is advantageous because it will not flake, disintegrate, or break down from contacting the molten steel during its initial heating irrespective of the rapid rate of pouring of the molten steel and resultant high thermal shock.

While I have shown and described certain preferred forms of the invention, it is apparent that the invention is capable of Variation and modification from the forms shown so that the scope thereof would be limited only by the proper scope of the claims `appended hereto.

I claim:

1. The method of direct casting of steel slabs, ingots, and billets Which comprises first providing a mold of the desired shape having a thin outer metal shell, preforming sheets of a heat resistant ceramic of not over 1A to 1%; inch in thickness, forming an inner layer for said shell by `adhesively securing preformed replaceable ceramic sheets to the shell to cover the inside of said shell, pouring the molten metal directly into the mold to contact the ceramic liner, and while pouring the metal continuously cooling the outer shell of the mold.

2. The method of direct casting of steel slabs, ingots, and fbillets, as recited in claim 1, in which the step of adhesively securing the replaceable preformed sheets to the inside of the shell includes the steps of forming perforations in the outer shell and forming adhesive keys between the shell and the liner at the perforations.

References Cited UNITED STATES PATENTS 3,039,158 6/1962 Mueller 249-201 X 3,210,812 10/1965 Berwick l64273 X 1,998,258 4/1935 Snook 164-282 X 2,772,459 12/1956 Wieland 164-138 X 3,085,303 4/1963 Steigerwald 249-112 X 3,151,366 10/1964 Fromson 164-73 I. SPENCER OVERHOLSER, Primary Examiner.

EUGENE MAR, Assistant Examiner.

U.S. Cl. XR. 

